An image processing apparatus such as an electronic camera that records and reproduces still and moving pictures using a semiconductor memory card as a recording medium is available on the market. Photography using a camera includes photography with the camera held in a vertical orientation (portrait photography) and photography with the camera held in a horizontal orientation (landscape photography). A group of images shot by a camera usually includes images having different orientations. There are also electronic cameras having a function such that when such a group of images is displayed, images that were shot so have the portrait orientation are rotated automatically to make their orientation agree with that of images that were shot in the landscape orientation.
A function for playing back a shot image after shooting is beneficial to the user of the electronic camera. Electronic cameras having a function for rotating a shot still image automatically by sensing the orientation of the camera held by the user are also already on the market.
It is known that if an image is rotated and displayed, more time is required to read image data from the memory card in comparison with a case where the display is presented without rotation. For this reason, as disclosed in the specification of Japanese Patent Application Laid-Open No. 07-320047, a technique has been proposed whereby rotation processing is executed after image data to be rotated has been reduced in size, thereby shortening data read-out time and reducing processing time required for rotating and displaying images.
FIG. 8 schematically illustrates this technique for shortening the time needed to rotate and display an image. First, original image data is reduced to make it conform to the display size (X pixels vertically and Y pixels horizontally) and then the image of reduced size is subjected to rotation processing.
Generally speaking, rotation processing is implemented by reading out data from noncontiguous addresses. It is known that for this reason, rotating and displaying an image takes approximately four times the processing time as compared with a case where an image is displayed without rotating it.
In order to deal with this, an image playback apparatus described in the specification of Japanese Patent Application Laid-Open No. 07-320047 contemplates shortening processing time by executing rotation processing after the still image to be rotated is reduced in size. However, since rotation processing usually is executed after the image has been reduced to a fixed size, a problem which arises is that successive changeover (frame advance) of images to be displayed cannot be performed smoothly.
Furthermore, a fixed period of time is required for rotation processing, as mentioned above, also with regard to processing during scrolling of part of the area of an image after the enlargement thereof. Consequently, reduction processing to a fixed size and rotation processing as in the prior art take time and smooth scrolling cannot be carried out.